In the recovery of oil from oil-bearing reservoirs, it usually is possible to recover only minor portions of the original oil in place by the so-called primary recovery methods which utilize only the natural forces present in the reservoir. Thus a variety of supplemental recovery techniques have been employed in order to increase the recovery of oil from subterranean reservoirs. The most widely used supplemental recovery technique is waterflooding which involves the injection of water into the reservoir. As the water moves through the reservoir, it acts to displace oil therein to a production system composed of one or more wells through which the oil is recovered.
It has long been recognized that factors such as the interfacial tension between the injected water and the reservoir oil, the relative mobilities of the reservoir oil and injected-water, and the wettability characteristics of the rock surfaces within the reservoir are factors which influence the amount of oil recovered by waterflooding. Thus it has been proposed to add surfactants to the flood water in order to lower the oil-water interfacial tension and/or to alter the wettability characteristics of the reservoir rock. Processes which involve the injection of aqueous surfactant solutions are commonly referred to as surfactant waterflooding or as low tension waterflooding, the latter term having reference to the mechanism involving the reduction of the oil-water interfacial tension. Also, it has been proposed to add viscosifiers such as polymeric thickening agents to all or part of the injected water in order to increase the viscosity thereof, thus decreasing the mobility ratio between the injected water and oil and improving the sweep efficiency of the waterflood.
A problem with stability and effectiveness arises when these surfactants and thickeners are used in environments characterized by high temperatures (e.g., 160.degree.-240.degree. F.), high pressures (e.g., up to 4000 psi), high concentrations of divalent and trivalent metal ions such as calcium, magnesium, boron, barium, iron, etc. (e.g., up to 3000 ppm or more and in some instances as high as 10,000 or 20,000 ppm), high salinity (e.g., when the floodwater is sea water), and low or high pH (e.g., pH in the range of about 3 to about 11).
Many waterflooding applications have employed anionic surfactants. For example, a paper by W. R. Foster entitled "A Low-Tension Waterflooding Process", Journal of Petroleum Technology, Vol. 25, February 1973, pp. 205-210, describes a technique involving the injection of an aqueous solution of petroleum sulfonates within designated equivalent weight ranges and under controlled conditions of salinity. The petroleum sulfonate slug is followed by a thickened water slug which contains a viscosifier such as a water-soluble biopolymer. This thickened water slug is then followed by a driving fluid such as a field brine which is injected as necessary to carry the process to conclusion.
One problem encountered in waterflooding with certain of the anionic surfactants such as the pertroleum sulfonates is the lack of stability of these surfactants in so-called "hard water" environments. These surfactants tend to precipitate from solution in the presence of even low concentrations of divalent metal ions such as calcium and magnesium ions. Typically, divalent metal ion concentrations of about 50-100 ppm and above tend to cause precipitation of the petroleum sulfonates.
Nonionic surfactants, such as polyethoxylated alkyl phenols, polyethoxylated aliphatic alcohols, carboxylic esters, carboxylic amides, and polyoxyethylene fatty acid amides, have a somewhat higher tolerance of polyvalent ions such as calcium or magnesium than do the more commonly utilized anionic surfactants. While it is technically feasible to employ a nonionic surfactant solution to decrease the interfacial tension between the injected aqueous displacing medium and petroleum contained in some limestone formations, such use would not be economically feasible for several reasons. Nonionic surfactants are not as effective on a per mole basis as are the more commonly used anionic surfactants, and furthermore, the nonionic surfactants have a higher cost per unit weight than do the anionic surfactants. Moreover, polyethoxylated alkyl phenol nonionic surfactants exhibit a reverse solubility relationship with temperature and become insoluble at temperatures of above about 125.degree. F. making them ineffective in many oil formations. Nonionic surfactants that remain soluble at elevated temperatures are generally not effective in reducing interfacial tension. Other types of nonionic surfactants hydrolyze at temperatures above about 165.degree. F.
The use of certain combinations of anionic and nonionic surfactant to combat hard water formations is also taught in the art. For example, U.S. Pat. No. 3,811,505 discloses the use of alkyl or alkylaryl sulfonates or phosphates and polyethoxylated alkyl phenols. U.S. Pat. No. 3,811,504 teaches the use of three component mixture including an alkyl or alkrylaryl sulfonate, an alkyl polyethoxy sulfate and a polyethoxylated alkyl phenol. U.S. Pat. No. 3,811,507 teaches the use of a water-soluble salt of a linear alkyl or alkylaryl sulfonate and a polyethoxylated alkyl sulfate.
Cationic surface active materials, such as, for example, quaternary ammoniums salts, derivatives of fatty amines and polyamines, have also been used. However, these compounds have the disadvantage of substantivity or attraction, especially towards silicate rock, and they lose their activity by adsorption.
The use of certain amphoteric surfactants which function as cationics in acid media and become anionic when incorporated in alkaline systems has been proposed. For Example, U.S. Pat. No. 3,939,911 discloses a surfactant waterflooding process employing a three-component surfactant system. The three-component surfactant system includes an alkyl or alkylaryl sulfonate such as an ammonium dodecyl benzene sulfonate, a phosphate ester sulfonate, and a sulfonated betaine such as a C.sub.12 -C.sub.24 alkyl amido C.sub.1 -C.sub.5 alkane dimethylammonium propane sulfonate. The several surfactant components may be employed in concentrations from about 0.05% to about 5.0% and preferably about 0.2% to about 0.5% by weight.
U.S. Pat. Nos. 4,076,743 and 4,090,969 disclose the use of compounds of the formula ##STR1## wherein R.sub.1 and R.sub.2 are aliphatic hydrocarbon radicals having 1 to 18 carbon atoms and/or hydrogen, wherein the sum of the carbon atoms of R.sub.1 and R.sub.2 is 9 to 18, R.sub.3 and R.sub.4 can be the same or different and represent lower alkyl or lower alkylol groups, X represents an integer of 2 to 4, y represents either 0 or 1, and z represents an integer of from 1 to 4. These compounds are disclosed as being useful as interfacial-active agents in flood water in the extraction of mineral oil and as having satisfactory solubility in formation water having a high salt content.
U.S. Pat. No. 4,130,491 discloses the use of compounds of the following formula in surfactant waterflooding: ##STR2## wherein R.sup.1 is an acid residue derived from the naphthenic acids; R.sup.2 is an alkylene residue with 2 to 6 carbon atoms; R.sup.3 and R.sup.4 may be the same or different and preferably represent a low molecular weight alkyl residue, especially a straight-chain alkyl residue with 1 to 4 carbon atoms; and R.sup.5 is an alkylene residue with preferably 1 to 3 carbon atoms.
U.S. Pat. No. 4,193,452 discloses the use in surfactant waterflooding of the combination of a C.sub.5 -C.sub.8 aliphatic alcohol with amphoteric sulfonate surfactants of the formulae ##STR3## wherein R.sub.1 is a hydrocarbyl group containing from 8 to 26 carbon atoms; R.sub.2 and R.sub.3 are each independently a hydrocarbyl group containing from 1 to 8 carbon atoms or an alkoxy group containing from 2 to 10 carbon atoms and having a ratio of carbon atoms to oxygen atoms within the range of 2 to 3; R.sub.4 is an aliphatic group containing from 1 to 6 carbon atoms; and R.sub.5, R.sub.6 and R.sub.7 are aliphatic hydrocarbyl groups containing in combination a total number of carbon atoms within the range of 17 to 24 and at least two of R.sub.5, R.sub.6 and R.sub.7 containing at least 8 carbon atoms.
U.S. Pat. No. 4,216,097 discloses the use in surfactant waterflooding of an amphoteric surfactant of the formula ##STR4## wherein R.sub.1 is a hydrocarbyl group containing from 8 to 26 carbon atoms; R.sub.2 and R.sub.3 are each independently a hydrocarbyl group containing from 1 to 8 carbon atoms or an alkoxy group containing from 2 to 10 carbon atoms and having a ratio of carbon atoms to oxygen atoms within the range of 2 to 3; R.sub.4 is an aliphatic group containing from 1 to 6 carbon atoms; and A is a sulfonate group or a carboxylate group.
U.S. Pat. No. 4,259,191 discloses the use in surfactant waterflooding of sulfobetaines of the formula ##STR5## wherein R.sup.1 is naphthenoyl residue derived from naphthenic acid; R.sup.2 is an alkylene residue with 2 to 6 carbon atoms; R.sup.3 and R.sup.4 are the same or different and are alkyl groups of 1 to 4 carbon atoms; R.sup.5 is an alkylene residue of 1-4 carbon atoms; and x is 0 or 1.
The use of thickening agents to increase the viscosity of injected water, normally to a value of at least equal to that of the reservoir oil, in order to arrive at a favorable mobility ratio between the oil and water and increase the macroscopic displacement efficiency of waterflood is known. Examples of such thickeners or mobility control agents are Polysaccharide B-1459 available from Kelco Company under the tradename "Kelzan" or the partially hydrolyzed polyacrylamides available from the Dow Chemical Company under the tradename "Pusher" chemicals. Problems have arisen with many of these thickeners. Some undergo a marked decrease in viscosity of relatively high temperatures and therefore are not sufficiently thermally stable for use in oil fields having relatively high temperatures (e.g., 160.degree.-240.degree. F.). Many are also relatively difficult to inject, have a relatively low tolerance to divalent and trivalent metal ions, and/or have poor shear stability.
While many surfactants and thickeners have been proposed for supplemental recovery use, there is a substantial, unfilled need for a surfactant/thickener system that is usable for recovering hydrocarbons from oil formations of high temperature, high salinity, high pressure, high concentrations of divalent and trivalent metal ions, and high or low pH.